Publication number | US7324433 B1 |

Publication type | Grant |

Application number | US 10/105,130 |

Publication date | Jan 29, 2008 |

Filing date | Mar 21, 2002 |

Priority date | Nov 29, 2001 |

Fee status | Paid |

Also published as | US7701871 |

Publication number | 10105130, 105130, US 7324433 B1, US 7324433B1, US-B1-7324433, US7324433 B1, US7324433B1 |

Inventors | Yungping Hsu, Ricky Cheung |

Original Assignee | Marvell International Ltd. |

Export Citation | BiBTeX, EndNote, RefMan |

Patent Citations (13), Non-Patent Citations (9), Referenced by (2), Classifications (8), Legal Events (4) | |

External Links: USPTO, USPTO Assignment, Espacenet | |

US 7324433 B1

Abstract

The present invention is directed to a method, program product, and apparatus that determines a signal quality associated with a symbol modulated signal based on a scalar relationship based on at least one of a comparison of plural correlation candidates for a symbol in the modulated signal or a comparison of the vector corresponding to a decided symbol against a reference. In accordance with one aspect of the present invention, a method and apparatus are disclosed which involve determining maximum and next-maximum correlation candidates for a symbol perceived in the modulated signal, calculating the scalar relationship between the maximum and next-maximum correlation candidates, and deriving a signal quality associated with the modulated signal based on the scalar relationship. In accordance with another aspect of the present invention, a method and apparatus are disclosed which involve determining a decided symbol for the symbol perceived in the modulated signal, calculating a scalar relationship between a vector corresponding to the decided symbol and a reference, and deriving a signal quality associated with the modulated signal based on the scalar relationship. In accordance with either of these aspects, the derived signal quality can be used to alter one or more receiver characteristics of a receiver used to capture the modulated signal.

Claims(72)

1. A method comprising:

determining maximum and next-maximum correlation candidates for a symbol perceived within a modulated signal;

calculating a scalar relationship between the maximum and next-maximum correlation candidates;

deriving a signal quality associated with the modulated signal based on the scalar relationship; and

altering a receiver characteristic based on said derived signal quality.

2. The method of claim 1 , wherein

the symbol is defined by a plurality of chips; and

wherein said determining step comprises:

correlating the chips of the symbol against a plurality of possible candidate vectors;

first selecting as the maximum correlation candidate one of the plurality of possible candidate vectors most correlated to the chips of the symbol pursuant to said correlating step; and

second selecting as the next-maximum correlation candidate at least one of the plurality of possible candidate vectors other than the maximum correlation candidate most relatively correlated to the chips of the symbol pursuant to said correlating step.

3. The method of claim 2 , further comprising deriving the plurality of possible candidate vectors from an ordered set of symbol vectors based on at least one characteristic of the modulated signal, the ordered set of symbol vectors being ordered according to a first order.

4. The method of claim 3 , wherein

said correlating step includes the step of generating a correlation parameter for each of the plurality of possible candidate vectors with respect to the chips of the symbol; and

wherein said first and second selecting steps comprises assessing the correlation parameters using one of:

a sequential comparison process following the first order; and

a modified sequential comparison process following a second order associated with the set of symbol vectors, the second order being dissimilar from the first order.

5. The method of claim 4 , wherein the second order is defined with respect to at least one subset of the set of symbol vectors, the subset including plural members of the set of symbol vectors selected in accordance with a relative distance relationship therebetween.

6. The method of claim 1 , wherein the symbol comprises a complementary code keyed symbol compliant with IEEE 802.11b (1999).

7. The method of claim 1 , wherein the scalar relationship comprises at least one of:

a distance between the maximum and next-maximum correlation candidates; and

a magnitude difference between the maximum and next-maximum correlation candidates.

8. The method of claim 1 , further comprising:

receiving the modulated signal in accordance with a receiver characteristic; and

modifying the receiver characteristic based on the derived signal quality.

9. A method comprising:

determining a decided symbol for a symbol perceived within a modulated signal;

calculating a scalar relationship between a vector corresponding to the decided symbol and a reference;

deriving a signal quality associated with the modulated signal based on the scalar relationship; and

altering a receiver characteristic based on said derived signal quality.

10. The method of claim 9 , wherein said deriving step comprises

comparing the scalar relationship to a threshold;

generating a first signal if the scalar relationship is less than the threshold; and

generating a second signal if the scalar relationship at least meets the threshold.

11. The method of claim 10 , further comprising:

receiving the modulated signal in accordance with a receiver characteristic; and

modifying the receiver characteristic based if the derived signal quality comprises the first signal.

12. The method of claim 9 , further comprising:

receiving the modulated signal in accordance with a receiver characteristic; and

modifying the receiver characteristic based on the derived signal quality.

13. The method of claim 9 , wherein the symbol comprises a complementary code keyed symbol complaint with IEEE 802.11b (1999).

14. A computer-readable storage medium that stores a program code that causes an information processor to perform at least the following steps, the steps comprising:

determining maximum and next-maximum correlation candidates for a symbol perceived within a modulated signal;

calculating a scalar relationship between the maximum and next-maximum correlation candidates;

deriving a signal quality associated with the modulated signal based on the scalar relationship; and

altering a receiver characteristic based on said derived signal quality.

15. The computer-readable storage medium of claim 14 , wherein

the symbol is defined by a plurality of chips; and

wherein said determining step comprises:

correlating the chips of the symbol against a plurality of possible candidate vectors;

first selecting as the maximum correlation candidate one of the plurality of possible candidate vectors most correlated to the chips of the symbol pursuant to said correlating step; and

second selecting as the next-maximum correlation candidate at least one of the plurality of possible candidate vectors other than the maximum correlation candidate most relatively correlated to the chips of the symbol pursuant to said correlating step.

16. The computer-readable storage medium of claim 15 , further comprising computer readable program code causing the information processor to perform deriving the plurality of possible candidate vectors from an ordered set of symbol vectors based on at least one characteristic of the modulated signal, the ordered set of symbol vectors being ordered according to a first order.

17. The computer-readable storage medium of claim 16 , wherein

said correlating step includes the step of generating a correlation parameter for each of the plurality of possible candidate vectors with respect to the chips of the symbol; and

wherein said first and second selecting steps comprises assessing the correlation parameters using one of:

a sequential comparison process following the first order; and

a modified sequential comparison process following a second order associated with the set of symbol vectors, the second order being dissimilar from the first order.

18. The computer-readable storage medium of claim 17 , wherein the second order is defined with respect to at least one subset of the set of symbol vectors, the subset including plural members of the set of symbol vectors selected in accordance with a relative distance relationship therebetween.

19. The computer-readable storage medium of claim 14 , wherein the symbol comprises a complementary code keyed symbol compliant with IEEE 802.11b (1999).

20. The computer-readable storage medium of claim 14 , wherein the scalar relationship comprises at least one of:

a distance between the maximum and next-maximum correlation candidates; and

a magnitude difference between the maximum and next-maximum correlation candidates.

21. The computer-readable storage medium of claim 14 , further comprising computer readable program code causing the information processor to perform at least the following additional steps, the steps comprising:

receiving the modulated signal in accordance with a receiver characteristic; and

modifying the receiver characteristic based on the derived signal quality.

22. A computer-readable storage medium that stores program code that causes an information processor to perform at least the following steps, the steps comprising:

determining a decided symbol for a symbol perceived within the modulated signal;

calculating a scalar relationship between a vector corresponding to the decided symbol and a reference;

deriving a signal quality associated with the modulated signal based on the scalar relationship; and

altering a receiver characteristic based on said derived signal quality.

23. The computer-readable storage medium of claim 22 , wherein said deriving step comprises comparing the scalar relationship to a threshold;

generating a first signal if the scalar relationship is less than the threshold; and

generating a second signal if the scalar relationship at least meets the threshold.

24. The computer-readable storage medium of claim 23 , further comprising computer readable program code causing the information processor to perform at least the following additional steps, the steps comprising:

receiving the modulated signal in accordance with a receiver characteristic; and

modifying the receiver characteristic based if the derived signal quality comprises the first signal.

25. The computer-readable storage medium of claim 22 , further comprising computer readable program code causing the information processor to perform at least the following additional steps, the steps comprising:

receiving the modulated signal in accordance with a receiver characteristic; and

modifying the receiver characteristic based if the derived signal quality comprises the first signal.

26. The computer-readable storage medium of claim 22 , wherein the symbol comprises a complementary code keyed symbol compliant with IEEE 802.11b (1999).

27. A symbol processor operable upon a symbol modulated signal, the symbol processor comprising:

a candidate determination unit to determine maximum and next-maximum correlation candidates for a symbol perceived within the modulated signal;

a scalar calculation unit coupled to said candidate determination unit to calculate a scalar relationship between the maximum and next-maximum correlation candidates;

a signal quality derivation unit coupled to said scalar calculation unit to derive a signal quality associated with the modulated signal based on the scalar relationship; and

at least one of a radio frequency (RF) unit and a media access controller (MAC) interface to alter a receiver characteristic based on said derived signal quality.

28. The symbol processor of claim 27 , wherein

the symbol is defined by a plurality of chips; and

wherein said candidate determination unit comprises:

a correlator to correlate the chips of the symbol against a plurality of possible candidate vectors; and

a comparator coupled to said correlator, the comparator capable of selecting as the maximum correlation candidate one of the plurality of possible candidate vectors most correlated to the chips of the symbol and capable of selecting as the next-maximum correlation candidate at least one of the plurality of possible candidate vectors other than the maximum correlation candidate most relatively correlated to the chips of the symbol.

29. The symbol processor of claim 28 , wherein the correlator further comprises a candidate manager to derive the plurality of possible candidate vectors from an ordered set of symbol vectors based on at least one characteristic of the modulated signal, the ordered set of symbol vectors being ordered according to a first order.

30. The symbol processor of claim 29 , wherein

said correlator includes a vector analysis unit coupled to said candidate selection logic to generate a correlation parameter for each of the plurality of possible candidate vectors with respect to the chips of the symbol; and

wherein said comparator comprises selection logic to assess the correlation parameters using one of:

a sequential comparison process following the first order; and

a modified sequential comparison process following a second order associated with the set of symbol vectors, the second order being dissimilar from the first order.

31. The symbol processor of claim 30 , wherein the second order is defined with respect to at least one subset of the set of symbol vectors, the subset including plural members of the set of symbol vectors selected in accordance with a relative distance relationship therebetween.

32. The symbol processor of claim 27 , wherein the symbol comprises a complementary code keyed symbol compliant with IEEE 802.11b (1999).

33. The symbol processor of claim 27 , wherein the scalar relationship comprises at least one of:

a distance between the maximum and next-maximum correlation candidates; and

a magnitude difference between the maximum and next-maximum correlation candidates.

34. The symbol processor of claim 27 , further comprising:

a decided symbol determination unit coupled to said scalar calculation unit to determine a decided symbol for the symbol perceived within the modulated signal; and

wherein said scalar calculation unit calculate a second scalar relationship between a vector corresponding to the decided symbol and a reference; and

wherein said signal quality derivation unit derives a second signal quality associated with the modulated signal based on the second scalar relationship.

35. The symbol processor of claim 34 , wherein said scalar calculation unit comprises a comparison unit coupled to said decided symbol determination unit to compare the scalar relationship to a threshold and generate one of a first signal if the second scalar relationship is less than the threshold and a second signal if the second scalar relationship at least meets the threshold.

36. A receiver, comprising:

a receive unit to receive a modulated signal in accordance with a receiver characteristic;

a symbol processor coupled to the receive unit, comprising:

a candidate determination unit to determine maximum and next-maximum correlation candidates for a symbol perceived within the modulated signal;

a scalar calculation unit coupled to said candidate determination unit to calculate a scalar relationship between the maximum and next-maximum correlation candidates; and

a signal quality derivation unit coupled to said scalar calculation unit to derive a signal quality associated with the modulated signal based on the scalar relationship; and

at least one of a radio frequency (RF) unit and a media access controller (MAC) interface to alter a receiver characteristic based on said derived signal quality.

37. The receiver of claim 36 , further comprising modification logic responsive to said symbol processor to modify the receiver characteristic based on the derived signal quality.

38. The receiver of claim 36 , wherein

the symbol is defined by a plurality of chips; and

wherein said candidate determination unit comprises:

a correlator to correlate the chips of the symbol against a plurality of possible candidate vectors; and

a comparator coupled to said correlator, the comparator capable of selecting as the maximum correlation candidate one of the plurality of possible candidate vectors most correlated to the chips of the symbol and capable of selecting as the next-maximum correlation candidate at least one of the plurality of possible candidate vectors other than the maximum correlation candidate most relatively correlated to the chips of the symbol.

39. The receiver of claim 38 , wherein the correlator further comprises a candidate manager to derive the plurality of possible candidate vectors from an ordered set of symbol vectors based on at least one characteristic of the modulated signal, the ordered set of symbol vectors being ordered according to a first order.

40. The receiver of claim 39 , wherein

said correlator includes a vector analysis unit coupled to said candidate selection logic to generate a correlation parameter for each of the plurality of possible candidate vectors with respect to the chips of the symbol; and

wherein said comparator comprises selection logic to assess the correlation parameters using one of:
a modified sequential comparison process following a second order associated with the set of symbol vectors, the second order being dissimilar from the first order.

a sequential comparison process following the first order; and

41. The receiver of claim 40 , wherein the second order is defined with respect to at least one subset of the set of symbol vectors, the subset including plural members of the set of symbol vectors selected in accordance with a relative distance relationship therebetween.

42. The receiver of claim 36 , wherein the symbol comprises a complementary code keyed symbol compliant with IEEE 802.11b (1999).

43. The receiver of claim 36 , wherein the scalar relationship comprises at least one of:

a distance between the maximum and next-maximum correlation candidates; and

a magnitude difference between the maximum and next-maximum correlation candidates.

44. The receiver of claim 36 , wherein said symbol processor further comprises:

a decided symbol determination unit coupled to said scalar calculation unit to determine a decided symbol for the symbol perceived within the modulated signal; and

wherein said scalar calculation unit calculates a second scalar relationship between a vector corresponding to the decided symbol and a reference; and

wherein said signal quality derivation unit derives a second signal quality associated with the modulated signal based on the second scalar relationship.

45. The receiver of claim 44 , wherein said scalar calculation unit comprises a comparison unit coupled to said decided symbol determination unit to compare the scalar relationship to a threshold and generate one of a first signal if the second scalar relationship is less than the threshold and a second signal if the second scalar relationship at least meets the threshold.

46. A transceiver, comprising:

a transmitter;

a receiver to receive a modulate signal in accordance with a receiver characteristic;

a symbol processor coupled to said receiver and said transmitter, said symbol processor comprising:

a candidate determination unit to determine maximum and next-maximum correlation candidates for a symbol perceived within the modulated signal;

a scalar calculation unit coupled to said candidate determination unit to calculate a scalar relationship between the maximum and next-maximum correlation candidates; and

a signal quality derivation unit coupled to said scalar calculation unit to derive a signal quality associated with the modulated signal based on the scalar relationship; and

at least one of a radio frequency (RF) unit and a media access controller (MAC) interface to alter a receiver characteristic based on said derived signal quality.

47. A base station, comprising:

an antenna;

a transmitter and a receiver coupled to said antenna, said receiver comprising:

a receive unit to receive a modulated signal in accordance with a receiver characteristic;

a symbol processor coupled to said receive unit, said symbol processor comprising:
a candidate determination unit to determine maximum and next-maximum correlation candidates for a symbol perceived within the modulated signal;
a signal quality derivation unit coupled to said scalar calculation unit to derive a signal quality associated with the modulated signal based on the scalar relationship; and
at least one of a radio frequency (RF) unit and a media access controller (MAC) interface to alter a receiver characteristic based on said derived signal quality.

a scalar calculation unit coupled to said candidate determination unit to calculate a scalar relationship between the maximum and next-maximum correlation candidates; and

48. A network interface, comprising:

a data interface;

a receiver coupled to said data interface, said receiver comprising:

a receive unit to receive a modulated signal in accordance with a receiver characteristic; and

a symbol processor coupled to said receive unit, said symbol processor comprising:
a candidate determination unit to determine maximum and next-maximum correlation candidates for a symbol perceived within the modulated signal;
a scalar calculation unit coupled to said candidate determination unit to calculate a scalar relationship between the maximum and next-maximum correlation candidates; and
a signal quality derivation unit coupled to said scalar calculation unit to derive a signal quality associated with the modulated signal based on the scalar relationship; and
at least one of a radio frequency (RF) unit and a media access controller (MAC) interface to alter a receiver characteristic based on said derived signal quality.

49. An information processing system, comprising:

an information processor coupled to a data interface;

a receiver coupled to said data interface, said receiver comprising

a receive unit to receive a modulated signal in accordance with a receiver characteristic; and

a symbol processor coupled to said receive unit, said symbol processor comprising:
a candidate determination unit to determine maximum and next-maximum correlation candidates for a symbol perceived within the modulated signal;
a scalar calculation unit coupled to said candidate determination unit to calculate a scalar relationship between the maximum and next-maximum correlation candidates; and
at least one of a radio frequency (RF) unit and a media access controller (MAC) interface to alter a receiver characteristic based on said derived signal quality.

signal quality derivation unit coupled to said scalar calculation unit to derive a signal quality associated with the modulated signal based on the scalar relationship; and

50. A symbol processor operable upon a symbol modulated signal, the symbol processor comprising:

means for determining maximum and next-maximum correlation candidates for a symbol perceived within the modulated signal;

means for calculation a scalar relationship between the maximum and next-maximum correlation candidates;

means for deriving a signal quality associated with the modulated signal based on the scalar relationship; and

means for altering a receiver characteristic based on said derived signal quality.

51. The symbol processor of claim 50 , wherein

the symbol is defined by a plurality of chips; and

wherein said determining means comprises:

means for correlating the chips of the symbol against a plurality of possible candidate vectors; and

means for selecting as the maximum correlation candidate one of the plurality of possible candidate vectors most correlated to the chips of the symbol and capable of selecting as the next-maximum correlation candidate at least one of the plurality of possible candidate vectors other than the maximum correlation candidate most relatively correlated to the chips of the symbol.

52. The symbol processor of claim 51 , further comprising means for deriving the plurality of possible candidate vectors from an ordered set of symbol vectors based on at least one characteristic of the modulated signal, the ordered set of symbol vectors being ordered according to a first order.

53. The symbol processor of claim 52 , wherein

said correlating means includes means for generating a correlation parameter for each of the plurality of possible candidate vectors with respect to the chips of the symbol; and

wherein said selecting means includes means for assessing the correlation parameters using one of:
a modified sequential comparison process following a second order associated with the set of symbol vectors, the second order being dissimilar from the first order.

a sequential comparison process following the first order; and

54. The symbol processor of claim 53 , wherein the second order is defined with respect to at least one subset of the set of symbol vectors, the subset including plural members of the set of symbol vectors selected in accordance with a relative distance relationship therebetween.

55. The symbol processor of claim 50 , wherein the symbol comprises a complementary code keyed symbol compliant with IEEE 802.11b (1999).

56. The symbol processor of claim 50 , wherein the scalar relationship comprises at least one of:

a distance between the maximum and next-maximum correlation candidates; and

a magnitude difference between the maximum and next-maximum correlation candidates.

57. The symbol processor of claim 50 , further comprising:

means for determining a decided symbol for the symbol perceived within the modulated signal;

means for calculating a second scalar relationship between a vector corresponding to the decided symbol and a reference; and

means for deriving a second signal quality associated with the modulated signal based on the second scalar relationship.

58. The symbol processor of claim 57 , wherein said second signal quality derivation means comprises

means for comparing the scalar relationship to a threshold; and

means for generating one of a first signal if the second scalar relationship is less than the threshold and a second signal if the second scalar relationship at least meets the threshold.

59. A receiver, comprising:

means for receiving a modulated signal in accordance with a receiver characteristic;

means for processing a symbol perceived within the modulated symbol, comprising:

means for determining maximum and next-maximum correlation candidates for the symbol;

means for calculating a scalar relationship between the maximum and next-maximum correlation candidates; and

means for deriving a signal quality associated with the modulated signal based on the scalar relationship; and

means for altering a receiver characteristic based on said derived signal quality.

60. The receiver of claim 59 , further comprising means for modifying the receiver characteristic based on the derived signal quality.

61. The receiver of claim 59 , wherein

the symbol is defined by a plurality of chips; and

wherein said determining means comprises:

means for correlating the chips of the symbol against a plurality of possible candidate vectors; and

means for selecting as the maximum correlation candidate one of the plurality of possible candidate vectors most correlated to the chips of the symbol and capable of selecting as the next-maximum correlation candidate at least one of the plurality of possible candidate vectors other than the maximum correlation candidate most relatively correlated to the chips of the symbol.

62. The receiver of claim 61 , wherein the correlating means further comprises means for deriving the plurality of possible candidate vectors from an ordered set of symbol vectors based on at least one characteristic of the modulated signal, the ordered set of symbol vectors being ordered according to a first order.

63. The receiver of claim 62 , wherein

said correlating means includes means for generating a correlation parameter for each of the plurality of possible candidate vectors with respect to the chips of the symbol; and

wherein said selecting means comprises means for assessing the correlation parameters using one of:
a modified sequential comparison process following a second order associated with the set of symbol vectors, the second order being dissimilar from the first order.

a sequential comparison process following the first order; and

64. The receiver of claim 63 , wherein the second order is defined with respect to at least one subset of the set of symbol vectors, the subset including plural members of the set of symbol vectors selected in accordance with a relative distance relationship therebetween.

65. The receiver of claim 59 , wherein the symbol comprises a complementary code keyed symbol compliant with IEEE 802.11b (1999).

66. The receiver of claim 59 , wherein the scalar relationship comprises at least one of:

a distance between the maximum and next-maximum correlation candidates; and

a magnitude difference between the maximum and next-maximum correlative candidates.

67. The receiver of claim 59 , wherein said symbol processing means further comprises:

means for determining a decided symbol for the symbol perceived within the modulated signal;

means for calculating a second scalar relationship between a vector corresponding to the decided symbol and a reference; and

means for deriving a second signal quality associated with the modulated signal based on the second scalar relationship.

68. The receiver of claim 67 , wherein said second signal quality deriving means comprises means for comparing the scalar relationship to a threshold and generating one of a first signal if the second scalar relationship is less than the threshold and a second signal if the second scalar relationship at least meets the threshold.

69. A transceiver, comprising:

means for transmitting a first modulated signal;

means for receiving a second modulated signal in accordance with a receiver characteristic;

means for processing a symbol perceived within the modulated symbol, comprising:

means for determining maximum and next-maximum correlation candidates for the symbol;

means for calculating a scalar relationship between the maximum and next-maximum correlation candidates; and

means for deriving a signal quality associated with the modulated signal based on the scalar relationship; and

means for altering a receiver characteristic based on said derived signal quality.

70. A base station, comprising:

means for transmitting and receiving a modulated signal, said receiving means comprising:

means for receiving the modulated signal in accordance with a receiver characteristic;

means for processing a symbol perceived within the modulated symbol, comprising:
means for deriving a signal quality associated with the modulated signal based on the scalar relationship; and

means for determining maximum and next-maximum correlation candidates for the symbol;

means for calculating a scalar relationship between the maximum and next-maximum correlation candidates; and

means for altering a receiver characteristic based on said derived signal quality.

71. A network interface, comprising:

means for transferring data;

means for receiving a modulated signal, comprising:
means for processing a symbol perceived within the modulated symbol, comprising:
means for calculating a scalar relationship between the maximum and next-maximum correlation candidates; and
means for deriving a signal quality associated with the modulated signal based on the scalar relationship; and

means for receiving the modulated signal in accordance with a receiver characteristic; and

means for determining maximum and next-maximum correlation candidates for the symbol;

means for altering a receiver characteristic based on said derived signal quality.

72. An information processing system, comprising:

means for processing information;

means for receiving a modulated signal responsive to said information processing means, said receiving means comprising:
means for processing a symbol perceived within the modulated symbol, comprising:
means for calculating a scalar relationship between the maximum and next-maximum correlation candidates; and
means for deriving a signal quality associated with the modulated signal based on the scalar relationship; and

means for receiving the modulated signal in accordance with a receiver characteristic; and

means for determining maximum and next-maximum correlation candidates for the symbol;

means for altering a receiver characteristic based on said derived signal quality.

Description

This application claims priority benefit under 35 U.S.C. § 119(e)(1) to U.S. Provisional Application No. 60/334,347, filed Nov. 29, 2001, entitled Method and Apparatus For Determining Signal Quality, which is incorporated herein fully by reference.

This invention is generally concerned with modulated signal receiver performance, and is particularly concerned with techniques for assessing perceived signal quality of a modulated signal derived from processing one or more coded symbols contained within the signal.

The past few years has witnessed the ever-increasing availability of relatively cheap, low power wireless data communication services, networks and devices, promising near wire speed transmission and reliability. One technology in particular, described in the IEEE Standard 802.11b-1999 Supplement to the ANSI/IEEE Standard 802.11, 1999 edition, collectively incorporated herein fully by reference, and more commonly referred to as “802.11b” or “WiFi”, has become the darling of the information technology industry and computer enthusiasts alike as a wired LAN/WAN alternative because of its potential 11 Mbps effective data transmission rate, ease of installation and use, and transceiver component costs make it a real and convenient alternative to wired 10 BaseT Ethernet and other cabled data networking alternatives. With 802.11b, workgroup-sized networks can now be deployed in a building in minutes, a campus in days instead of weeks since the demanding task of pulling cable and wiring existing structures is eliminated. Moreover, 802.11b compliant wireless networking equipment is backwards compatible with the earlier 802.11 1 M/2 Mbps standard, thereby further reducing deployment costs in legacy wireless systems.

802.11b achieves relatively high payload data transmission rates through the use of orthogonal class modulation in general, and, more particularly, 8-chip complementary code keying (“CCK”) as a 11 MHz chipping rate. As such, bitstream data is mapped into nearly orthogonal sequences (or code symbols) to be transmitted, where each chip of the code symbol is quaternary phase modulated. An 801.11b compliant receiver correlates the received CCK modulated signal with 64 candidate waveforms to find the most likely code symbol, from which the bitstream data is recovered through reverse mapping. The high-rate physical layer PLCP preamble and header portions are still modulated using the 801.11 compliant Barker spreading sequence at an 11 MHz chipping rate, resulting in a 1 or 2 Mbps effective header and preamble transmission rate depending on whether DBPSK or DQPSK modulation is employed.

CCK was chosen in part because of its strong inherent resistance to multipath interference, which is likely to be encountered in the typical in-building deployment. Nevertheless, the confluence of strict power/noise limits specified for operation in the 2.4 GHz ISM band and megabit+expected data throughput rates limits conventional 802.11b to just a 100 or so feet between stations, depending on the number of interposing radio obstructions and reflections.

Thus 802.11b remains susceptible to multipath interference, and to reception errors produced by inter-symbol (“ISI”) and inter-chip interference(“ICI”) in particular. To combat this, designers have sought to improve receiver performance, at least with respect to CCK code symbol demodulation by using active equalization techniques. However, such techniques do not appear to take into account symbol processing reliability or errors, much less track such errors, nor alter the transmission environment when post symbol processing signal quality degrades.

To address these and other perceived shortcomings, the present invention is directed to a method, program product, and apparatus that determines a signal quality associated with a symbol modulated signal based on a scalar relationship based on at least one of a comparison of plural correlation candidate for a symbol in the modulated signal or a comparison of the vector corresponding to a decided symbol against a reference. In accordance with one aspect of the present invention, a method and apparatus are disclosed which involve determining maximum and next-maximum correlation candidates for a symbol perceived in the modulated signal, calculating the scalar relationship between the maximum and next-maximum correlation candidates, and deriving a signal quality associated with the modulated signal based on the scalar relationship.

In accordance with another aspect of the present invention, a method and apparatus are disclosed which involve determining a decided symbol for the symbol perceived in the modulated signal, calculating a scalar relationship between a vector corresponding to the decided symbol and a reference, and deriving a signal quality associated with the modulated signal based on the scalar relationship.

In accordance with either of these aspects, the derived signal quality can be used to alter one or more receiver characteristics of a receiver used to capture the modulated signal.

Additional aspects and advantages of this invention will be apparent from the following detailed description of preferred embodiments thereof, which proceeds with reference to the accompanying drawings.

**100** including an antenna and a data interface according to an embodiment of the invention.

**220** shown in

Turning first to **100** including an antenna **105** and data interface (e.g. MAC interface **160**) according to an embodiment of the invention. This transceiver can form an operational part of a base station, network interface, or an information processing system as is well known in the art. As such, the transceiver includes duplex RF unit **110** for receiving and transmitting IEEE 802.11b Physical Layer Convergence Procedure (“PLCP”) sublayer frames modulated onto a selected carrier frequency in the Industrial, Scientific and Medical (“ISM”) band—2.4 Ghz as is well-known in the art via antenna **105**. Though not shown in the figure, RF Unit **110** of the present embodiment includes selective diversity tuning circuitry and gain control to assist in tailoring RF unit **110** receiver performance in commonly encountered noisy or multipath environments. Also as part of the RF unit **110** are RF and IF frequency up/down converters used in modulating a baseband signal onto the selected carrier frequency for transmission, as well as receiving and extracting the baseband signal **115** (in analog form) from a tuned channel in the ISM band.

The ADC**120** and pulse-shaping FIR **130** complement the functions of the RF unit **110** in a known manner to convert the inbound and still analog baseband signal **115** into chipped digital form **125** suitable for coded symbol recognition, demodulation and processing gain signal quality determination consistent with the present invention as performed by the receive symbol processor **140**.

It should be noted here that the digital baseband signal **125** presents the data of interest in the form of one or more coded symbols following one or more coding protocols, still requires further processing before e.g. received data can be extracted for use by a Media Access Controller (“MAC”, not shown) and higher layers and applications executing on e.g. a local or remote information processor (not shown). To this end, the receive symbol processor **140** handles symbol decoding/demodulation functions consistent with 802.11b coding protocols, including Barker spreading and the aforementioned CCK protocols. In turn, consistent with the IEEE 802.11 and 802.11b standards, the descrambler **150** de-whitens inbound data recovered from the symbol processor **140** for delivery to a data interface such as the layer **2** MAC interface **160**, the MAC itself and the aforementioned higher layers.

The transmit pathway includes the scrambler **155** that whitens outbound data presented by the MAC interface **160** on behalf of the MAC or higher layer protocols and applications it supports. The so-whitened outbound data is then coded, modulated and transmitted in sequence by the remaining components of the transmit pathway by the transmit symbol processor **145**(encodes whitened outbound data the using one of the aforementioned symbol modulation techniques depending on the selected transmission rate), FIR **135** and DAC **126** (converts the so-coded outbound data to analog baseband form) and the RF modulator (not shown) and transmitter (not shown) of the RF unit **110**.

The receive pathway, namely the receiver components of RF unit **110** (not shown), the ADC **120**, the FIR **130**, the receive symbol processor **140**, and the descrambler **150** could be implemented in an alternative embodiment as a discrete receiver coupled to the MAC interface **160**. Likewise, the aforementioned components of the transceiver transmit pathway can be implemented as a discrete transmitter coupled to the MAC interface **160**.

Also, in this embodiment, the receive symbol processor **140** is responsible for determining and maintaining signal quality perceived at the post-processing or symbol decode/demodulation stage. In particular, the receive symbol processor **140** includes a signal quality derivation unit (**270**, to be discussed in more detail with reference to **2**”) to the MAC and higher layers, applications and/or services (collectively “MAC+layers”) which the transceiver **100** supports via MAC interface **160**. In an alternative embodiment, the receive symbol processor **140** may communicate with the MAC interface **160** “in-band” by including the signal quality information within the data decoded from one or more given symbols it delivers to the scrambler **150**.

In the embodiment shown in **160**, the receive symbol processor **140** may also direct the RF unit **110** to alter one or more characteristics of the receiver environment within the command of the RF unit **110** (such as diversity tuning and/or gain control) in an effort to redress poor signal quality as reflected by e.g. SQ**2**. The receive symbol processor **140** does so by issuing an appropriate directive (labeled RF_CNTL) directly to the RF unit **110**. In an alternative embodiment, the symbol processor may include the directive in-band as part of outband data that is coded and delivered to the FIR **130**/DAC **120** tandem and then onto the RF unit **110**.

A more detailed discussion of the relevant functions and composition of the receive symbol processor **140** according to the embodiment shown in **140** according to the present embodiment. As shown in **232** (used to decide a Barker encoded symbol in the digital chipped baseband signal **125**); 2) the candidate determination unit **225** (determines the maximum correlation and next-maximum correlation candidates as well as the decided CCK encoded symbol based on such candidates found in the signal **125**); 3) a scalar calculation unit **286** which uses decided symbol and correlation candidate information to calculate a scalar relationship; and 4) a signal quality derivation unit **270** to derive a signal quality associated with the signal **125** from the scalar relationship(s) calculated by the scalar calculation unit **286**. More detail on the composition and function of each of these components will be discussed in greater detail below.

Turning first to the determination units **232** and **235**, the digital chipped baseband signal **125** is serially presented (on a per chip basis) by FIR **130** to the demux **210**, where based on the expected modulation type (“mod_type” in **230** of the decided symbol determination unit **232** or the CCK correlator **220** of the candidate determination unit **225**. In particular, if the current symbol is positioned within the PLCP header or preamble, or represents PLCP frame payload (e.g. MAC Payload Data Unit or MPDU) modulated at 802.11 base rates (1 Mbps or 2 Mbps), such symbol is decoded using a Barker mode demodulation pathway (Barker correlator **230** in combination with RAKE filter **240**) with the decided symbol determination unit **232**. If, however, the symbol represents high-rate (e.g. 5.5 or 11 Mbps) PLCP payload/MPDU data, the symbol is instead decoded using a CCK demodulation pathway DFE **212**, serial-to-parallel latch **214**, CCK correlator **220** and comparator **250** collectively within the candidate determination unit **225**.

Considering first the situation where Barker demodulation is needed, the Barker correlator **230**-RAKE filter **240** produces a decided symbol in complex vector form (Re+jIm), as is well-known in the art. This decided symbol is labeled in **240** presents the decided symbol vector to the DQPSK demodulator **260** for convectional phase decoding considerations as well as the scalar calculation unit **286** and specifically to comparison unit **274** thereof. The fully symbol decoded data is generated by the DQPSK demodulator **260** and sent to the descrambler to regenerate user data bits (i.e. the data of interest).

The comparison unit **274** of the scalar calculates unit **286** assesses the Barker mode decided symbol in this embodiment by comparing the magnitudes of the real and imaginary parts of the decided symbol vector against one of two selectable thresholds, Th1 (for DBPSK 1 Mbps transmission rate) and Th2 (for DQPSK 2 Mbps transmission rate) In one implementation, Th1 is 0.25 and Th2 is 0.375. Thus, if the magnitude of either the real or imaginary components of the deiced symbol is less than Th1 or Th2 respectively, it is determined that the post-processing signal quality has degraded and so comparison unit **274** yields true and a counter **278** of the signal quality derivation unit **270** (accessed via mux **276**) is incremented. Also, in this embodiment, the MAC I/F **160** and MAC+layers serviced by the transceiver **110** are notified of the signal quality degradation through issuance of the SQ**2** signal by the SQ**2** control unit **284** of the signal quality derivation unit **270**. Alteratively, other techniques for apprising external resources of the perceived degradation in signal quality may be used, such as making the contents of the counter **278** accessible upon request or sending an appropriate message downstream as part of or in addition to the decoded data sent to descramble **150**.

Considering now where the current symbol is CCK-encoded (i.e. mod_type=CCK), the CCK denudation pathway of the candidate determination unit **225** is instead selected. Still referring to **210** to the decision feedback equalizer **212** for equalization purposes and then on to serial to parallel latch **214**. Digital feedback equalization techniques such as disclosed in U.S. patent application Ser. No. 10/080,826, filed Feb. 21, 2002, entitled DECODING METHOD AND APPARATUS which is incorporated herein fully by reference, may be used here.

Once all chips defining the current CCK modulated symbol have been equalized and accumulated by the latch **214**, the latch releases them in parallel to the CCK correlator **220** of the candidate determination unit **225**. The CCK correlator **220** correlates the chips of the current symbol against a plurality of possible candidate vectors, each representing a possible CCK symbol to decide which symbol was received. The plurality of possible candidate vectors is defined here as a subset of the ordered set of 64 CCK symbol vectors selected based on at least one characteristic of the modulated signal bearing the symbol of interest, such as the CCK modulation transmission rate (here either 5.5 Mbps or 11 Mbps, labeled as tran_rate(CCK) in

Consistent with the present embodiment, several techniques may be used to single out the possible candidate vectors, including parallel correction against the entire set of CCK symbol vectors followed by selective comparison of correlation results involving only the possible candidate vectors, flagging the possible candidates presented in a larger table accommodating the entire set of CCK symbol vectors and correcting only these candidates against the latched symbol chips, etc. Herein, the set of CCK symbol vectors may be conveniently set forth in a lookup table such as vector table (“VT”) **224** within or accessible to the CCK correlator **220**, and the subset of possible candidate vectors may be flagged therein by an internal candidate manager agent **222**.

Though not required, the CCK correlator **220** and more specifically the vector analysis unit **226** thereof here correlates the chips of the symbol by computing the dot product between these chips and at least the possible candidate vectors. A resulting correlation parameter is generated by this unit **226** for each of the possible candidate vectors, consisting of the sum of the real and imaginary scalar results of the dot product process. As is known in the art, the candidate vector whose correlation parameter has the higher value is considered to be the “most correlated vector”, the “best match” or the “maximum correlation candidate” (as is used herein and labeled “MAX” in **2**-d**7**, and along with data bits d**0**-d**1** resolved by the DQPSK demodulator **260**, completes the data octet corresponding to the current CCK symbol. This octet is sent to the descrambler **150** to complete recovery of the data in a known manner.

More detail on correlation processing may be found in e.g. U.S. patent application Ser. No. 10/092,971, filed Mar. 5, 2002naming Guorong Hu, Yungping Hsu, and Weishi Feng as co-inventors and entitled METHOD AND APPARATUS FOR COMPLEMENTARY CODE KEYING, which is incorporated herein fully by reference.

As discussed above, signal quality consistent with the present embodiment may be realized through comparative vector analysis of the maximum correlation candidate and the next-maximum correlation candidate(s), defined herein as one or more possible candidate vectors having the relatively next-highest correction parameter value(labeled “MAX**2**”). In particular, a scalar relationship between the maximum and next-maximum correlation candidates is calculated in order to derive the measure of signal quality.

To better understand the relationship between the maximum correlation candidate and the next-maximum correlation candidate, consider a sample plot of correlation parameter produced by a CCK correlator **220** on a complex plane, wherein angle φ1=1+j, φ2=φ3=φ4=0 at 11 Mbps transmission rate, as depicted in **500**), each of 18 next-maximum correlation candidate vectors (not every matching correlation parameter is shown) has a correlation parameter of 8 (e.g. |8|+|0|—point **505**, |4|+|4|—point **510**, |0|+|8|—point **515**, |−4|+|4|—point **520**, |4|+|−4|—point **525** along outer diamond **530**. In addition, there are 8 possible candidate vectors with a correlation parameter of 4 (e.g. points **550**, **555**, **560**, **565** along inner diamond **570**), and finally 37 candidates **580** with a correlation parameter of 0. Details of how to find the next-maximum correlation candidate in accordance with the present embodiment will be discussed below with reference to

In the embodiment of **286** and the comparison unit **280** thereof, in particular, calculates a scalar relationship for the current CCK encoded symbol signal quality for CCK encoded symbols by comparing the difference between the correlation parameters generated by the vector analysis unit **226** of the CCK correlator **220** for the maximum and next-maximum correlation candidates with a preselected threshold, here Th5.5 as 0.5 (5.5 Mbps transmission rate) and Th11 (11 Mbps transmission rate) as 0.375. If this difference (a type of scalar relationship) is less than the respective threshold based on the present transmission rate, the signal quality is perceived to have degraded and the comparison unit **280** instructs the counter **278** of the signal quality derivation unit **270** to increment (again through mux **276**). Likewise, the SQ**2** control unit **284** of the signal quality derivation unit **270** notifies the MAC interface **160** either directly or indirectly that the signal quality has degraded, and may, upon direction of the MAC or higher layers or applications the transceiver is servicing, may direct the RF unit **110** to alter one or more receiver characteristics.

It should be noted that the components of the receive symbol processor **140**, including but not limited to, the aforementioned decided symbol determination unit **232**, the candidate determination unit **225**, the scalar calculation unit **286**, and the signal quality derivation unit **270**, in the embodiment depicted in **232**, **225**, **286**, and **270** or as specified in the flowchart of

Although not shown in the figures, consistent with the present embodiment the MAC+layers serviced by the transceiver **100** may communicate with the corresponding transmitter (transmitter generating the inbound carrier signal) to alter transmit characteristics such as power level and/or transmission rate in an effort to improve signal quality. It may do so by embedding appropriate messages in the e.g. MPDU or PLCP preamble/header portions that the corresponding transmitter PHY or MAC may decode, as one with ordaining skill in the art will appreciate. Moreover, the SQ**2** control unit **284** may inform these higher layer services and applications that the signal quality has improved, if for example, it is determined that the calculated scalar relationship in either mode exceeds the appropriate threshold.

Moreover, although the present embodiment contemplates certain types of scalar relationships (e.g. Barker mode—magnitude of the real and imaginary components of the decided symbol vector which is essentially a scalar difference between the decided symbol vector and nil, or CCK mode—difference in correlation parameters for the maximum and next-maximum correlation candidates), other types of scalar relationships may be used consistent with the present invention in order to derive an appropriate measure of signal quality based on perceived processing gain reliability and/or errors. For example, in CCK mode, a scalar or Euclidean distance between maximum and next-maximum correlation candidate vectors may be calculated and thresholded to determine if there's signal quality problem (again a higher number indicates a more reliable correlation decision has been reached.

Turning now to **140** may include an ASIC and/or a programmed information processor such as a microporocccor or microcontroller designed to execute the sequence of steps described in the flowchart of **140** described above.

**250** which leverages the relative distance characteristics of CCK referred to herein as modified sequential comparison processing. First, consider a brute-force or sequential comparison processing in which the correlation parameters generated by the CCK correlation **220** are compared in squential CCK symbol vector order to find the maximum correlation candidate from the subset of possible candidate vectors, which is the case of 11 Mbps transmission rate, requires comparison of 64 correlation parameters. Thus, 63 comparisons must be made to find the maximum correlation candidate. Then, one or more of the next maximum correlation candidates may be found by disregarding the correlation parameter for the maximum correlation candidate and again looking for those possible candidate vectors which have the largest remaining correction parameters. Using this technique, another 62 comparisons must be made.

However, by exploiting relative distance relationships within subsets of CCK vectors, one can group together and re-order comparions according to a second order (depicted as order **401**, **411**, **421**, **431** handled by group selection logic **408**, **418**, **428**, or **438** respectively). Again assuming the subset of possible candidate vectors corresponds with the 64 member set of CCK symbol vectors, comparison can be localized to within 4 groups (**400**, **410**, **420** and **430**) of 16 sequential vectors (**0**-**15**, **16**-**31**, **32**-**47**, and **48**-**63**) differentiated by the value of φ3 using the aforementioned group selection logic **408**, **418**, **428**, and **438** respectively, and can be further localized within each 16 vector group to 4 subgroups of four vector comparisons. Because of this grouping approach and the reordered initial comparisons, each four vector comparison subgroup cannot provide both the maximum and the next maximum correlation candidate, since each vector in each subgroup are “uncorrelated” with each other—in other words, they are defined by a relative maximum Euclidean distance from another. If one of the vectors in one of these subgroups is found to be MAX, it is very unlikely that MAX**2** will be in this subgroup. By using this approach, the total number of comparisons can be reduced from 125 to 73.

Consider first the set of possible candidate vectors defined where φ3=0. In this case, group of vectors **0**-**15** (group **400**) are compared out of sequence using order **401** provided by group selection logic **408**. As shown in **0**, **2**, **8**, **10** (subgroup **402**), **1**, **3**, **9**, **11** (subgroup **403**), **4**, **6**, **12**, **14** (subgroup **404**), and **5**, **7**, **13**, **15** (subgroup **405**). For each subgroup, the correlation parameters of the first two and the last two members are compared (e.g. **0**-**2** and **8**-**10** for subgroup **402**, **1**-**3** and **9**-**11** for subgroup **403**, **4**-**6** and **12**-**14** for subgroup **404** and **5**-**7** and **13**-**15** for subgroup **405**), and then the larger of each pair is then compared to find a subgroup maximum correlation parameter. The local maximum and next maximum correlation parameters (labeled as max_{—}0 and max2_{—}0 in **400** are then selected using sequential comparison of the four subgroup maximum correlation parameters.

The local maximum for the remaining vector groups **410**, **420**, and **430** can be then determined in sequence taking into consideration the following observations. First, except for the first group **400**, the local maximum and next maximum (max_{—}1, max2_{—}1 in group **410**; max_{—}2, max2_{—}2 in group **420**; max_{—}3, max2_{—}3) are selected using sequential comparison taking into account the respective four subgroup maximum correlation parameters along with the max and max**2** correlation parameters from the immediately preceding group. For example, in the case of vector group **410**, the subgroup maximum correlation parameters for subgroups **412**, **413**, **414**, and **415** are sequentially compared against the max_{—}0 and max2_{—}0 values to find the max_{—}1 and max2_{—}1 correlation parameters.

According to this embodiment, the modified sequential comparison process continues until the maximum max_{—}3 and next maximum max2_{—}3 correlation parameters are obtained with reference to subgroup **430**. In this process, the possible candidate vector corresponding to the max_{—}3 correlation parameter is deemed the maximum correlation candidate and the possible candidate vector(s) corresponding to the max2_{—}3 correlation parameter are deemed the next maximum correction candidate.

It will be obvious to those having ordinary skill in the art that many changes may be made to the details of the above-described embodiments of this invention without departing from the underlying principles thereof. For example, though the above-described embodiments are directed to implementations compliant with IEEE 802.11 and 802.11b standard, the teachings of the present invention are not intended to be so limiting and in fact post symbol processing signal quality consistent with the present invention can be derived in other coded symbol reception scenarios and environments, whether based on RF transmission or otherwise. The scope of the present invention should, therefore, be determined only by the following claims.

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Classifications

U.S. Classification | 370/208, 370/479, 370/342, 375/142, 375/150 |

International Classification | H04J11/00 |

Cooperative Classification | H04W28/18 |

European Classification | H04W28/18 |

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